Electrophotographic recording material

ABSTRACT

This invention realtes to an electrophotographic recording material consisting of an electroconductive support material and a photoconductive double layer of organic materials which consists of a homogeneous, opaque, charge carrier producing dyestuff layer from a compound of the general formula   IN WHICH X1 and X2 are identical or different and stand for -NHor -S- and Ar and Ar&#39;&#39; may be substituted, such compunds being particularly suitable as are substituted in peri position to the C O, -S- or -NH-group in the five-membered ring and of a transparent top layer of insulating materials with at least one charge transporting compound.

United States Patent Wiedemann [451 Oct. 1, 1974 ELECTROPHOTOGRAPHIC RECORDING 1 MATERIAL Wolfgang Wiedemann, Geisenheim-Johannisberg, Germany Assignee: Kalle Aktiengesellschaft,

WiesbadenBiebrich, Germany Filed: Apr. 25, 1973 Appl. No.: 354,201

[75] Inventor:

[30] Foreign Application Priority Data July 31,1972 Germany 2237680 US. Cl. 96/15, 96/ 1.6 Int. Cl 603g 5/06 Field of Search 96/1.5, 11.6

[56] References Cited UNITED STATES PATENTS 3,573,906 4/1971 Goffe 96/15 Primary Examiner-Ronald H. Smith ,il i l m ne 7 1? B amm .c Attorney, Agent, 'or FirmJames E. Bryan, Esq.

:ST57]" ABSTRACT This invention realtes to an electrophotographic recording material consisting of an electroconductive support material and a photoconductive double layer of organic materials which consists of a homogeneous, opaque, charge carrier producing dyestuff layer from a compound of the general formula Xi Ar I Ar in which X and X are identical or different and stand for NH or S and Ar and Ar may be substituted, such compunds being particularly suitable as are substituted in peri position to the =C=O, S or v Nl-lgroup in the five-membered ring and of a transparent top layer of insulating materials with at least one charge transporting compound.

16 Claims, 3 Drawing Figures 600 70.0 llnm PAIENTEDBBT m 3,839,034

SHEU 10F 6 7 v Fig.1

Fig.2

{PAIENT num 11914 O J 5 M.

sum 2 or 6 PATENTEDBBT Hm 3.889.034

SHEET 30F 6 FOR MULAE (5 s w H 2 @7" II I H S Cl 0 PAIENIEnucr 11974 3.839.034

sum nor 6 FORMULAE PAIENTEDUET 111114v 7 sum 50F e I FORMULAE mmrrnw H 4 3.839.034 I SHEET 6 OF 6 FORMULAE H H Cl c1 O 0 Br H H Br N 17 s I Br Br 0 This invention relates to an electrophotographic recording material consisting of an electroconductive support material and a photoconductive double layer of organic materials which consists of a homogeneous, opaque, charge carrier producing dyestuff layer from a compound of the general formula O X1 4% Ar in which X and X are identical or different and stand for NH- or -S and Ar and Ar may be subsituted, such compounds being particularly suitable as are substituted in peri position to the =C=O, S or NH-group in the five-membered ring and of a transparent top layer of insulating materials with at least one charge transporting compound.

It is known from German Offenlegungsschriften Nos, 1,597,877 and 1,797,342 for electrophotographic recording material to extend the spectral sensitivity of selenium layers to the red spectral range by a double layer arrangement, e.g., with phthalocyanine dispersion layers. Disadvantageous are the vacuum vapor depositions of selenium requiring high technical expenditure, the brittleness of comparatively thick selenium layers, the poor adhesion of adjacent heterogeneous constituents in these layers and the only difficulty realizable uniformly wetting coating with the corresponding dispersions. Furthermore, no optimum light-sensitivities can be achieved as a result of the absorption behaviour and the different charge conducting mechanisms of selenium and phthalocyanine in the double layer arrangement.

From US. Pat. No. 3,5 73,906, for example, there are also known photoconductive double layers containing an organic, possibly photoconductive, insulating layer between the support material and the vapor-deposited selenium layer in order to impart adhesion. Such a layer construction, however, considerably hinders the necessary charge transport so that, in this casetoo, no higher light-sensitivities are obtainable.

Furthermore, from German Auslegeschrift No. 1,964,817, it is known to provide vapor-deposited selenium layers with a layer of an organic, photoconductive insulating material which is substantially insensitive to light in the visible range of the spectrum. According to German Offenlegungsschrift No. 2,l20,912, it has also been suggested to use those light-sensitive layer arrangements for electrophotographic recording materials which contain, as the charge carrier producing layer, an inorganic material, such as the sulfide, selenide, sulfoselenide or telluride of cadmium or zinc, and as the charge carrier transporting layer, an organic material with at least per cent by weight of 2,4,7-trinitro-9-fluorenone. A disadvantage of the production of these layers with inorganic photoconductors is the exact observation of the vapor deposition conditions of selenium or the exact adjustment of the mixtures in order to obtain a good photoconductive modification of the inorganic materials. Furthermore, the adhesion of selenium to conductive support material, such as to aluminum, is insufficient. Fatigue in repeated charge/exposure cycles does not allow the use in electrophotographic copying devices. v

Japanese Patent Application No. 43-26710 already discloses photoconductive double layers of organic materials on a conductive support. According to that application, a lower, relatively thick layer of a considerably'diluted homogeneous solution of a sensitizer in a binder is provided with an upper transparent lightsensitive layer. This layer construction, however, only offers a relatively low sensitivity increase only little meeting technical demands. Another known suggestion according to German Offenlegungsschrift No. 1,909,742 is to repeatedly pour a sensitizer solution over a photoconductive layer and to evaporate the solvent. A disadvantage thereof is the low mechanical resistance of the applied layer as a result of insufficient cohesion and adhesion of the applied sensitizer. Furthermore, repeated coating is cumbersome.

The construction of photoconductive double layers containing a dyestuff layer is also known, e.g. from Belgian Patents Nos. 763,389 and 763,541, but for this layer construction, top layers are used which allow no sensitivities satisfying highest demands and, as regards adhesion between the dyestuff layer and the top layer, do not represent an optimation and are not sufficiently resistant to mechanical attack, e.g., in electrophotographic copying devices, particularly to that due to the cleaning of the photoconductive layer.

It is the object of the present invention to provide an organic photoconductor layer highly light-sensitive for the xerograohic copying procedure which overcomes the described disadvantages and the adhesion of which between the various layers satisfies the highest technical demands, which exhibits no wear or fatigue and which, even after repeated use, may be used again rapidly.

The present invention provides an electrophotographic recording material consisting of an electroconductive support material with a photoconductive double layer of organic materials which consists of a homogeneous, opaque, charge carrier producing dyestuff layer from a compound of the general formula in which X, and X2 are identical or different and stand for NH- or S- and Ar and Ar may be substituted, such compounds being particularly suitable as are substituted in peri position to the =C=O, S- or NH- group in the five membered ring and of a transparent top layer of insulating materials with at least one charge transporting compound and is characterized in that the transparent top layer consists of a charge transporting, monomer, heterocyclic compound substituted by at least one dialkyl amino group or two alkoxy groups and having an extended 1r electron system or of a condensation product from 3-bromopyrene and formaldehyde and of a binder.

By means of the invention, it is possible to obtain highly light-sensitive, photoconductive double layers for the electrophotographic recording material of the invention which have a high mechanical resistance and may be arranged on a cylindrical drum, for example, or may circulate as an endless belt without exhibiting special signs of wear and thus are very suitable for the use in electrophotographic copying devices. The high lightsensitivity particuarly results from the 'fact that the charge transporting compound present in the transparent top layer is sensitized by the charge carrier producing dyestuff layer in that the charge carriers, such as electrons or holes are taken by the top layer.

In a preferred embodiment, the organic dyestuff layer has a thickness in the range from about 0.005 to about 2am. High concentration of excited dyestuff molecules is achieved thereby in the dyestuff layer and at the boundary surface between the dyestuff layer and the top layer. It has proved that layer thicknesses from about 0.005 to about lum are entirely sufficient and that even layers in the range of about 0.001 ,urn may be effective. Furthermore, the adhesion between the electroconductive support material and the top layer is not impaired.

In a preferred embodiment, the transparent top layers has a thickness in the range from about 5 to about 20p.'r n. Thisassures a sufficiently high charge.

The assembly of the electrophotographic recording material can be seen in the attached FIGS. 1 and 2.

FIG. 1 shows'a material which consists of an electroconductive layer support 1, the organic dyestuff layer 2, and the organic, transparent top layer 3. FIG. 2 shows a metallized plastic layer 1, 4 as the layer support to which a charge carrier injection inhibiting intermediatelayer is applied and the photoconductive double layer from organic dyestuff layer 2 and organic, transparent top layer 3 is on this intermediate layer.

Suitable electroconductive support materials are materials which hitherto have been used for this purpose, for example aluminum foils or transparent plastic supports to which aluminum, gold, copper, zinc, cadmium, indium, antimony, bismuth, tin, lead or nickel has been laminated or applied by vapor deposition.

As shown in FIG. 2, an organic intermdiate layer or a thermally, anodically or chemically produced metal oxide layer, e.g., aluminum oxide layer, may be applied to the electroconductive support material. This layer serves to decrease or to prevent charge carrier injection in the dark from the electroconductive support material into the organic dyestuff layer. On the other hand, it may not hinder, however, the flowing off of chargeduring exposure to light. Furthermore, the intermediate layer provides for a favorable influence of the adhesion of the organic dyestuff or double layer to the support material. Suitable as organic intermediate layers are various natural or synthetic resin binders which firmly adhere to a metal or aluminum surface and, upon subsequent application of the other layers, are not dissolved. Polyamide resins or polyvinyl phosphonic acid are particularly suitable for this purpose.

The thickness of the organic intermediate layer is in the range of about l,u.m, that of a metal oxide layer in the range from to 10 angstroms.

The organic dystuff layer of the recording material of the invention substantially determines the spectral light-sensitivity of the photoconductive double layer of the invention. The dyestuffs used are known compounds described in the Color Index, 2nd edition (1956), volume 3. Such dyestuffs are, for example, those listed in the attached formula table.

The meanings are as follows:

Formula No. Name C.I.

I Indigo 73.000 2 Thioindigo. Algol Red 5B 73.300 3 lndanthren Printing Red 3B 73.305 4 lndanthren Brilliant Pink R 73.360 5 lndanthren Red Violet RH 73.385 6 Indazin Bordeaux RRL 73.395 7 Permanent Red Violet MR Pigment Red 8X 8 Algol Orange RF 73.335 9 lndanthren Brilliant Pink 38 73.365 l0 Indanthren Scarlet B 73.355 II \(at Violet RR 73.600 12 Algol Violet BBN 73.605 l3 lndanthren Printing Violet BBF 73.595 14 lndanthren Printing Brown R 73.665 l5 Indanthren Brown RRD 73.4l0 l6 Brilliant Indigo B 73040 I7 Brilliant Indigo 48 73.065

processes or the gun spray method. The applicationpreferably is performed, however, by vapor depositing the dyestuff in the vacuum. A tightly packed coating is achieved thereby.

The tightly packed coating makes it unnecessary" to produce thick dyestuff layers for achieving a high absorption. I The tightly packed dyestuff molecules and the extremely low layer thickness permit. in'a particularly advantageous manner, the transport of charge carriers so that it is completelysufficient to produce the charge carriers at the boundary layer only.

The application of the dyestuff layer by vapor deposition in the vacuum requires dyestuffs with thermal resistivity in the temperature range to be applied for vapor deposition. The high extinction of the dyestuff allows high concentration of excited dyestuff molecules. Excitation (l) and charge separation (2) take place in the dyestuff layer according to the following reaction equations:

S dyestuff molecule S excited dyestuff molecule, and

-S ,-S dyestuff radical ions.

At the boundary surface between the organic dyestuff layer andthe transparent top layer, reactions of the excited dyestuff moelcules or the resulting charge carriers in the form of the dyestuff radical ions with the molecules of the charge transfer effecting compound in the top layer are possible according to the following equations:

with

F donor molecule F acceptor molecule -F F{- donor or acceptor radical ion At the boundary surface, sensitizing reactions take place between the transparent top layer and the organic dyestuff layer. The top layer thus is a sensitized organic photoconductor at least in the area or the boundary surface, which leads to the surprisingly high photoconductivity.

Reactions 3 and 5 proceed preferably when the rr-electron system in the top layer is a compound which, as a donor compound, easily can release electrons. This is the case with 2,5-bis-(4-diethylaminophenyl-oxiazole-l,3,4, for example. But also heterocyclic compounds with only one dialkyl amino group are suitable for rapid procedure of reactions 3 and 5. Reactions 4 and 6 are preferably possible with a substance in the top layer which, as an electron acceptor easily accepts electrons, e.g. 2,4,7-trinitrofluorenone or 3,6- dinitro-N-t-butyl-naphthalimide.

By means of the specific embodiment of the invention it is sufficient for the efficiency of the dyestuff when, besides its intense absorption, it only has either electron-attracting substituents, e.g. C O, NO halogen, or electron-repelling substitutents, e.g. alkyl or O-alkyl, depending on whether it is preferably suitable for reactions 3, 5 or 4, 6.

The invention permits charge carrier transport fostered by a particularly low expenditure of energy within the tightly packed dyestuff layer according to the following reactions:

7. 'S +S S+'S or 8. S -S -S In all conventional sensitizing processes, however, transport via the dyestuff molecules present in low concentration is impeded by their large distance from one another. Analogous is the charge transport in the top layer with: g

9. 'F F F +-F, (p-conductive) 10. 'F F F 'F (n-conductive) The practical consequence of reactions 1 to 10 is that, in the use of electron donors in the top layer, the I. double layer arrangement is negatively charged so that reactions 3, 5, 8, 9 can proceed. In the inverse case, layers with electron acceptors in the top layer are positively charged so that reactions 4, 6, 7 and 10 can proceed.

The transparent top layer or organic insulating materials with at least one charge transporting compound is described as follows:

The transparent top layer has a high electric resistance and prevents in the dark the flowing off of the electrostatic charge. Upon exposure to light, it transports the charges produced in the organic dyestuff layer.

In the case of negative charge, the transparent top layer preferably consists of a mixture of an electron donor compound and a binder. But when the electrophotographic recording material is to be used for positive charge the transparent top layer consists of a mixture of an electron acceptor compound and a binder.

Consequently, in the transparent top layer there are used compounds for charge transport which are known as electron donors or electron acceptors. They are used together with binders or adhesives adapted to the compound for charge transport as regards charge transport, film property, adhesion, and surface characteristics. Furthermore, conventional sensitizers or substances forming charge transfer complexes are preferably additionally present. But they can only be used in so far as the necessary transparency of the top layer is not impaired. Finally, other usual additives such as levelling agents, plasticizers, and-adhesives may also be present.

Suitable compounds for charge transport are especially those organic compounds which have an extended rr-electron system, e.g., monomer aromatic heterocyclic compounds.

Monomers employed in accordance with the invention are those which have at least one dialkyl amino group or two alkoxy groups. Particularly proved have heterocyclic compounds, such as oxidazole derivatives, which are mentioned in German Patent No. 1,058,836. An example thereof is in particular the 2,5-bis-(p-diethylaminophenyl)-oxdiazole-1,3,4, Further suitable monomer electron donor compounds are, for example, triphenyl amine derivatives, benzo-condensed heterocycles, pyrazoline or imidazole derivatives, as well as triazole and oxazole derivatives, e.g. 2-phenyl-4(2- chlorophenyl)-5-(4-diethylaminophenyl)-oxazole, as disclosed in German Patents Nos. 1,060,260, and 1,120,875. Formaldehyde condensation products with various aromates, e.g., condensates from formaldehyde and 3-bromopyrene, are also suitable.

Besides these mentioned compounds having predominatly a p-conductive character, it is also possible to use n-conductive compounds. These so-called electron acceptors are known from German Patent No. 1,127,218, for example. Compounds such as 2,4,7- trinitrofluorenone or N-t-butyl-3,6-dinitronaphthalimide have proved particularly suitable.

Suitable binders with regard to flexibility, film properties, and adhesion are natural and synthetic resins. Examples thereof are in particular polyester resins, e.g., those marketed under the names Dynapol (Dynamit Nobel), Vitel (Goodyear), and which are copolyesters of isoand terephthalic acid with glycol. Silicone resins are those known under the name SR of General Electric Comp., USA, or Dow 804 of Dow Corning Corp., USA, and representing three-dimensionally cross-linked phenyl-methyl siloxanes or so-called reactive resins as those known as DD lacquers and composed of an equivalent mixture of hydroxyl groups containing polyesters or polyethers and polyfunctional isocyanates, e.g. Desmophen and Desmodur of Bayer AG, Leverkusen, Germany, have proved particularly suitable. Furthermore, copolymers of styrene and maleic acid anhydride, e.g. those known under the name Lytron Monsanto Chemical Comp., USA, but also polycarbonate resins, e.g. those known under the name Lexan Grade of General Electric Comp., USA, are suitable for use.

The mixing ratio of charge transporting compound to binder may vary. Relatively certain limits are given, however, by the requirement for maximum photosensitivity, i.e., for the biggest possible portion of charge transporting compound, and for crystallization to be prevented, i.e., for the biggest possible portion of binder. A mixing ratio of about 1:1 parts by weight has proved preferably, but mixing ratios from about 3:1 to 1:4 or above, depending on the particular case, are also suitable.

The conventional sensitizers to be used additionally may advantageously foster charge transport. Moreover, they may produce charge carriers in the transparent top layers. Suitable sensitizers are, for example, Rhodamine B extra, Schultz, Farbstofftabellen (dyestuff tables), 1st volume, 7th edition, 1931, No. 864, page 365, Brilliant Green, No. 760, page 314, Crystal Violet, No. 785, page 329, and Cryptocyanine, No. 927, page 397. In the same sense as act the sensitizers may also act added compounds which form charge transfer complexes with the charge transporting compound. Thus, it is possible to achieve another increase of the photosensitivity of the described double layers. The qunatity of added sensitizer or of the compound forming the charge transfer complex is so determined that the resulting donor acceptor complex with its charge transfer band still is sufficiently transparent for the organic dyestuff layer below. Optimum concentration is at a molar donor/acceptor ratio of about 10:1 to about 100:1 and vice versa.

The addition of adhesives as binders to the charge transporting compounds already yields a good photosensitivity. In this case, low-molecular polyester resin, such as Adhesive 49 000, Du Pont, has proved particularly suitable.

1n the described manner, the top layers have the property to render possible a high charge with a small dark discharge. Whereas in all conventional sensitizations an increase of the photosensitivity is connected with an increase of the dark current, the arrangement of the invention can prevent this parallelity. The layers are thus usable in electrophotographic copying devices with low copying speeds and very small lamp energies as well as in those with high copying speeds and correspondingly high lamp energies.

The top layers are prepared according to the usual coating methods, e.g., whirl-coating, doctoring, kisscoating.

The invention will be further illustrated by way of the attached drawings.

Preparation of the dyestuff layers:

The dyestuffs listed in Table l are vapor deposited by a vacuum pump (Type A 1 of Pfeiffer, Wetzlar, Germany) at a reduced pressure of 10 to 10 mm Hg onto a 100p.m thick aluminum foil arranged at a distance o bo t m. Th .vator stepes i ate y t i ture is measured directly at the surface of the dyestuff to be vapor deposited by means of a NiCrthermoelement. The layer weight of the vapor deposited dyestuff is in the range from about 0.01 to l glm Table 1 Dyestuff No. Vapor deposition Time Temperature (min) (C) lndigo l 0.5 180 Thioindigo 2 l 230 lndanthren Printing Red 38 3 2 270 lndanthren Brilliant Pink R 4 2 270 lndazin Bordeaux RRL 6 2 230 Permanent Red Violet MR 7 2 300 Vat Violet RR 11 l 230 lndanthren Printing Violet BBF 13 l 270 lndanthren Brown RRD l5 3 350 Example 1 Homogeneous dyestuff layers, from thioindigo dyestuffs, which have been obtained by vapor deposition as described in Table 1 or under analogous conditions are coated with a solution from 1 part by weight of 2,5-bis-(4-diethylaminophenyl)- oxadiazole-1,3,4 and 1 part by weight of polyester resin, e.g. Dynapol L 206 of Dynamit Nobel AG, Troisdorf, Germany, in tetrahydrofurane as the solvent. After drying for 5 minutes at C, the thickness of the top layer is about 9 to 1 lum.

The photosensitivities of these double layers are summarized in Table 2.

They are determined accoring to the following method: On a slowly rotating disk, the photoconductor layer moves through a charging device (corona adjustment 7.0 kV, grid 1.5 kV.) to the exposure section where it is exposed to an Osram xenon lamp, type XBO 150. A heat absorbing glass, (type KG 3 of Schott & Gen., Mainz, Germany) and a neutral filter of 15 per cent transparency are placed before the lamp so that the light intensity in the plane of measurement is about 750 uW/cm? The charge height (U and the curve of the photo-induced light decay are oscillographically recorded by an electrometer (type 610 CR of Keithley Instruments, USA) through a transparent probe. The determination of the charge height (U in volts and of the half time (T in milliseconds yields the following results for the double layers as well as for a correspondingly prepared top layer without dyestuff (zero layer):

toplayer. 3 93 -Continued -Continued W No. Double layer Formula U,,(V) T AU Double layer U,,(V) TU2 with dyestuff No. Negative (msec) with dyestuff negative charge charge (msec) Formula No. 9 875 19 4 lndanthren Brilliant Pink R/ lndanthren Brilliant top layer 4 1,075 16 80 Pink R Formula No. 4 800 3| 5 lndanthren Red Violet RH/ to la er 5 1,200 22 50 p y The trisubstituted oxazole der1vat1ve prepared by 6 q f l reacting 4-diethylamino-2-chloro-benzoine with ben- Brllllant Pmk 3B/ 66 top layer 9 1,050 12 95 zonitrile according to H. Krauch and W. Kunze, Reaktionen der Organischem Chemie, 3rd edition, 1966, 7 Permanent Red a e 335 Violet MR/ 15 P g t 1 7 925 16 135 op ayer Example 3 8 Al 10 RF i, 8 900 80 70 Ind1g0 dyestuffs and asymmetrical 1nd1gold dyestuffs 9 d h yield the following photosensitivities in the double 1 2:; If, 20 layer arrangement of the invention with a top layer as top layer 10 1,075 68 70 described in Example 1:

The determination of the dark decay (AU is important for the use of the photoconductor layers in xerographic copying machines. This value is thus included in Table 2. It shows how rapidly a photoconductor layer is discharged in the dark after period of 2 seconds, after it has achieved its maximum charge. The dark decay is measured by a Dyn-Test 90 apparatus of ECE, Giessen, Germany. The spectral light sensitivity of the double layer with dyestuff No. 9 is measured as follows: The half time (T is determined for each wave length range at negative charge by exposure to a xenon lamp, type XBO 150, and placing therebefore monochromatic filters (line filters, half time width 10 to 12 nm, Schott & Gen., Mainz, Germany). By plotting the reciprocal values of the product from half time T (seconds) and light intensity Raw/cm versus the wave length A (nm), the spectral light sensitivity of the double layer is obtained which is shown in the attached FIG. 3. The reciprocal value of T I means the light energy calculated per unit area which has to be irradiated in order to discharge the layer to half its initial voltage U Example 2 Double layer U,,(V) T with dyestuff negative charge (msec) Zero layer 900 500 Permanent Red Violet MR Formula No. 7 600 23 lndanthren Brilliant Pink 38 (Measurement in analogy with Example 1; 615 uW/cm in the plane of measurement) Double layer Formula No. U,,(V) T with dyestuff negative charge (msee) Indigo 1 1.500 230 Vat Violet RR 11 1,100 27 Algol Violet BEN 12 1.050 40 Zero layer 800 280 Example 4 lndazin Bordeaux RRL (Formula No. 6 of Cassella Farbwerke Mainkur AG, Frankfurt/Main, Germany), lndanthren Brown RRD (Formula No 15) and lndanthren Printing Brown R (Formula No. 14) of Farbwerke Hoechst AG, Frankfurt/Hochst, Germany, yield the following photosensitivities in vapor deposited dyestuff layers at a top layer according to the Example 1: (Measuring method as in Example 2, 615 W/cm xenon lamp) For comparison purposes, a dyestuff layer vapor deposited with lndanthren Brilliant Pink 38 (formula 9) and one vapor deposited with Permanent Red Violet MR (Formula 7) are whirl-coated with a solution from polyvinyl carbazole, e.g. Luvican M of BASF, Ludwigshafen, Germany, and 18.6 per cent by weight of an adhesive polyester resin, e.g. Adhesive 49,000 of Du Pont, USA, in tetrahydrofurane-as the solvent so that after drying the layer thicknesses of the top layers are 6 and 10pm, respectively. The photosensitivity is determined as in Example 1; (light intensity 615 p.W/cm in the plane of measurement, xenon lamp).

Double layer top layer U,,(V) T with dyestuff No. thicknessutm) negative charge (msec) 3B 9 6 800 280 10 800 365 MR 7 6 760 410 10 875 585 Zero layer 6 50 1,000

Example 6 Double layer U ,(V) T with dyestuff negative charge (msec) lndanthren Brilliant 650 145 Pink 38, Formula No. 9

lndanthren Brilliant Pink R, Formula No. 4 700 215 Permanent Red Violet MR, Formula No. 7 675 157 Zero Layer 650 465 Example 7 c. three-dimensionally cross-linked phenylmethyl siloxane, e.g. silicone resin SR 182, 60 per cent in toluene, of General Electric Comp, USA

The photo-sensitivity of the homogeneous, glossy double layers is determined as in Example 1. (xenon lamp, light intensity 615 #W/cm Double luyer Binder used U,.(V) T with dyestuff in top layer negative charge (msec) Permanent Red Violet MR a 825 29 -Continued Double layer Binder used U,,(V) T with dyestuft in top layer negative charge (msec) lndanthren Red Violet RH a 925 47 b 875 52 c 800 32 Example 8 Equivalent quantities of a polyester containing hydroxyl groups, e.g. Desmophen 1100 (2g), and of a polyfunctional isocyanate, e.g. Desmodur HL (3 g), are applied together with 2,5-bis-(4-diethylaminophenyl)- oxadiazole-1,3,4 in tetrahydrofurane to dyestuff layers I from Permanent Red Violet MR (Formula 7) and lndanthren Brilliant Pink 38 (Formula 9) in a thickness of about 10pm. After drying and hardening for about 5 to 15 minutes at 120C, glossy, homogeneous top layers are obtained.

The photosensitivity is determined as in Example 1 (xenon lamp, light intensity 615 uW/cm Dyestuff UAV) i AU!) negative (msec) charge Permanent Red Violet MR 650 19 120 lndanthren Brilliant Pink 38 835 20 Example 9 A 2 per cent solution from a polyamide resin, e.g. Elvamide 8061 of Du Pont, USA, in trichloroethylenelmethanol (1:1) is coated on a polyester film (IOOum) vapor-deposited with aluminum. The thickness of the top layer is below lIJJI'l since the layer weight is 0.2 g/m To this organic intermediate layer, there are vapordeposited various dyestuffs, such as lndazin Bordeaux RRL (Formula 6) or Vat Violet RR (Formula 11) in analogy with Example 1. To this layer, there is applied a top layer as described in Example 1; after drying, the layer thickness is about 9 to 10am.

The photosensitivity is measured according to the method indicated in Example 1 (light intensity about 615 tw/cm xenon lamp).

Dyestuff layers from lndanthren Printing Violet BBF (Formula 13) are coated with solutions from a. 1 part by weight of 2,5-bis-(4-diethylaminophenyl)-oxadiazole-l,3,4 and 1 part by weight of polyester resin, e.g. Dynapol L 206 of Dynamit Nobel AG, Troisdorf, Germany, b. same as a) plus 10 part by weight of Green 0. same as a) plus 0.1 part by weight of 3,5- 5

dinitrobenzoic acid. The thicknesses of the top layers are about am.

The following photosensitivities are determined: (measuring method as in Example 1, xenon lamp, light Brilliant deposition o nto a aluminum foil (100 ,um) at 200 and 270C under a reduced pressure of 10 to 10" mm Hg.

These layers are coated with a solution as described in Example 1. After drying, the layer thicknesses are about 10pm.

The photosensitivity is determined as in Example 1 (xenon lamp, light intensity: 487 uW/cm Double layer U,,(V) T with dyestuff negative charge (msec) Brilliant indigo B 1,050 92 Brilliant indigo 4B l,l50 39 It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. An electrophotographic recording material consisting of an electro-conductive support material and a photoconductive double layer of organic materials which consists of a homogeneous, opaque, chargecarrier producing dyestuff layer from a compound of the general formula in which X and X are identical or different and stand for -NH or -S-- and Ar and Ar maybe substituted, such compounds being particularly suitable as are substituted in peri position to the =C==O, S or NH group in the five-membered ring, and of a transparent top layer of insulating materials with at least one charge transporting compound, in which the transparent top layer consists of a charge transporting, monomeric, heterocyclic compound substituted by at least one dialkyl amino group or two alkoxy groups and having an extended rr-electron system or of a condensation product from 3-bromopyrene and formaldehyde and of a binder.

2. A material according to claim 1, in which the heterocyclic compound is selected from the group of oxazoles, oxadiazoles, triazoles, imidazoles, and pyrazoles.

3. A material according to claim 1, in which the heterocyclic compound is an oxadiazole.

4. A material according to claim 1, in which the heterocyclic compound is 2,5-bis-(4diethylaminophenyl)- oxadiazolel ,3 ,4.

5. A material according to claim 1, in which the hoterocyclic compound is an oxazole.

6. A material according to claim 1, in which the heterocyclic compound is 2-phenyl-4-(2-chlorophenyl)-5- (4-diethylaminophenyl)-oxazole.

7. A material according to claim 1, in whichthe dyestuff layer has a thickness from about 0.005 to about 2am and the transparent top layer a thickness from about 5 to 20pm.

8. A material according to claim 1, in which the transparent top layer consists of a mixture of the charge transporting compound and the binder in a ratio by weight of about 1:1.

9. A material according to claim 1, in which the binder is selected from the group of polyesters, copolyesters, silicone resins, reactive resins from polyethers or polyesters and polyfunctional isocyanags gg polymers of styrene with maleic acid anhydride, and of polycarbonates.

10. A material according to claim 1, in which the binder is a copolymer from isoand terephthalic acid and a glycol.

11. A material according to claim 1, in which the binder is a copolymer from styrene and maleic acid anhydride.

12. A material according to claim 1, in which the binder is a reactive resin from polyethers or polyesters and polyfunctional isocyanates.

13. A material according to claim 1, in which the binder is asilicone resin from three-dimensionally cross linked phenyl methyl siloxane.

14. A material according to claim 1, in which the binder is a polycarbonate resin.

15. A material according to claim 1, in which the transparent top layer additionally contains sensitizers and/or substances forming charge transfer complexes.

16. A material according to claim 1, in which the photoconductive double layer is above an insulating intermediate layer on the support material. 

2. A material according to claim 1, in which the heterocyclic compound is selected from the group of oxazoles, oxadiazoles, triazoles, imidazoles, and pyrazoles.
 3. A material according to claim 1, in which the heterocyclic compound is an oxadiazole.
 4. A material according to claim 1, in which the heterocyclic compound is 2,5-bis-(4diethylaminophenyl)-oxadiazole-1,3,4.
 5. A material according to claim 1, in which the heterocyclic compound is an oxazole.
 6. A material according to claim 1, in which the heterocyclic compound is 2-phenyl-4-(2-chlorophenyl)-5-(4-diethylaminophenyl)-oxazole.
 7. A material according to claim 1, in which the dyestuff layer has a thickness from about 0.005 to about 2 Mu m and the transparent top layer a thickness from about 5 to 20 Mu m.
 8. A material according to claim 1, in which the transparent top layer consists of a mixture of the charge transporting compound and the binder in a ratio by weight of about 1:1.
 9. A material according to claim 1, in which the binder is selected from the group of polyesters, copolyesters, silicone resins, reactive resins from polyethers or polyesters and polyfunctional isocyanates, of copolymers of styrene with maleic acid anhydride, and of polycarbonates.
 10. A material according to claim 1, in which the binder is a copolymer from iso- and terephthalic acid and a glycol.
 11. A material according to claim 1, in which the binder is a copolymer from styrene and maleic acid anhydride.
 12. A material according to claim 1, in which the binder is a reactive resin from polyethers or polyesters and polyfunctional isocyanates.
 13. A material according to claim 1, in which the binder is a silicone resin from three-dimensionally cross-linked phenyl methyl siloxane.
 14. A material according to claim 1, in which the binder is a polycarbonate resin.
 15. A material according to claim 1, in which the transparent top layer additionally contains sensitizers and/or substances forming charge transfer complexes.
 16. A material according to claim 1, in which the photoconductive double layer is above an insulating intermediate layer on the support material. 